Journal of University of Chinese Academy of Sciences

Environmental impact of bauxite residue：a comprehensive review

XUE Shengguo, LI Yubing, GUO Ying

2017, 34 (4): 401-412. DOI: 10.7523/j.issn.2095-6134.2017.04.001

Bauxite residue is a solid waste in the industrial process of aluminum oxide, and it is characterized by high alkalinity and salinity and has no large volume of utilization. Presently, bauxite residue is still stored or dumped on land. The high rate of bauxite residue spill and pollution episode and the impact of bauxite residue seriously threaten sustainable development of alumina industry. On the basis of reviewing the literature in recent 30 years, this review summarizes the physical properties, chemical properties, and biological toxicity, focuses on the four dimensions of environmental impacts of bauxite residue, including the chronic and potential problems of disposal, utilization, and revegetation, and emphasizes the acute and sudden environmental risk to surrounding soil, water, and ecosystem with a typical bauxite residue repository failure case. Given the concerned problems of disposal and utilization of bauxite residue, future research directions are also discussed in this paper. This will provide a scientific reference for the large-scale disposal of bauxite residue and ecological rehabilitation, and ensure the healthy development of alumina industry.

Joint source channel symbol-level en/decoding fast algorithm based on space policy trellis

WANG Qiang, ZHANG Can, GAO Shaoshuai, TU Guofang

2017, 34 (4): 413-421. DOI: 10.7523/j.issn.2095-6134.2017.04.002

Abstract ( 293 ) PDF (KB) ( 2 )

Joint source channel symbol-level en/decoding fast algorithm based on space policy trellis is presented in this paper. Constructing a joint decoding plane trellis achieves better decoding performance than the bit-level decoding method. However, the complicated construction of plane trellis causes a high degree of complexity of the joint source channel symbol-level decoding. In this work, we construct a new efficient space policy trellis, optimize design of weight value of variable-length symbols by meeting the constraint condition system of equation, and then form an integrated fast algorithms with VLS-APP decoding. The results of two kinds of simulations indicate that our fast algorithm leads to near 50% reduction of the decoding complexity and lowers bit error rate in the same SNR of channels, compared to the decoding method based on plane trellis. So this method provides reliable error-protection mechanism for variable-length encoded information data, and it can be applied in joint source channel symbol-level en/decoding under resource-constrained situation like the space communication.

Target detection performance analysis of single illumination and triple observation passive radar

ZHOU Jianwei, LI Daojing, HU Xuan

2017, 34 (4): 422-430. DOI: 10.7523/j.issn.2095-6134.2017.04.003

Abstract ( 300 ) PDF (KB) ( 1 )

This work discusses the main problem and system loss in the aerial target detection system of omnidirectional passive radar. For the operation modes of radar system in SISO (single illumination and single observation) and in SITO (single illumination and triple observations), the detection ranges and measurement accuracies are analyzed under the condition that the numbers of array elements are the same. The target velocity expression is derived in SITO, and the accuracy of target velocity measurement is also discussed. The results show that SISO and SITO have about the same covering areas under certain conditions. Fortunately, SITO has the characteristics of high plane positioning accuracy, target velocity solvability, and low level of difficulty in technical implementation.

Sample optimization based on local features in speech emotion recognition

SUI Xiaoyun, ZHU Tingshao, WANG Jingying

2017, 34 (4): 431-438. DOI: 10.7523/j.issn.2095-6134.2017.04.004

Abstract ( 396 ) PDF (KB) ( 2 )

Emotion recognition is one of the most prospective technics in human-machine interaction process. Most researches prefer statistical functional features because these features are more consistent with the speech variation as emotion changes. However, local features, i.e., short-term or temporal features extracted from single frame also contain useful information. In this work, a new approach is proposed to optimize samples via local features. To achieve this, a K-means cluster is employed to cluster each sample with 2 groups: frames with obvious emotion and frames with emotion which is not that obvious. It is hypothesized that the cluster with more frames should be emotionally obvious. It is observed in the results that the classification performs better on optimized samples than on original ones. The method was tested on 3 corpora and the classification accuracy increases by 5%-17%. It is also found the improvement increases as speech length grows, which implies the optimization approach may be more applicable to the longer speech recognition.

Big data analysis of status and trends of global change research

MAO Ping, HUANG Dongxiao, WANG Yuhua, ZHOU Hua, WANG Haiyan, CHEN Huai

2017, 34 (4): 441-451. DOI: 10.7523/j.issn.2095-6134.2017.04.006

Abstract ( 519 ) PDF (KB) ( 3 )

To investigate the develop trends and the hot spots of the global change research, we used TDA analyzer to data mining based on WOS (Web of science) core collection database. We found that the annual number of publications increased rapidly in recent years, and a total of 145 849 papers were published in this field. The numbers of publications and citations in USA were far higher than those in other countries. However, the Chinese Academy of Sciences published 5 815 papers and was in the first rank of all the institutions. The research areas in the global change are mainly in environmental science and ecology, geography, meteorology, and atmospheric science, focusing on global warming, greenhouse gas effect, carbon and nitrogen cycle, biodiversity conservation, and sustainable development by using remote sensing, satellites, models, and GIS.

Future trends in carbon use efficiency for Chinese terrestrial ecosystem based on CMIP5 model results

YUAN Minshu, LI Mingxu, CHENG Hongyan, DING Juhua, LI Hanwei, PENG Changhui, ZHU Qiuan

2017, 34 (4): 452-461. DOI: 10.7523/j.issn.2095-6134.2017.04.007

Abstract ( 418 ) PDF (KB) ( 1 )

The datasets of gross primary production, net primary production, mean annual precipitation, and mean annual temperate were collected from the results of 12 models in Phase 5 of Coupled Model Intercomparison Project to investigate the temporal patterns of carbon use efficiency (CUE) for Chinese terrestrial ecosystem and the relationship between CUE and climate factors under different emission scenarios (RCP2.6, RCP4.5, and RCP8.5) from 2006 to 2100. Our results showed that the CUE from the different models for Chinese terrestrial ecosystem ranged from 0.332 to 0.617 with a mean level of 0.5 under the three scenarios. Slight decreasing trends were detected for CUE and these trends were enhanced by increasing radiation force. Future CUE of Chinese terrestrial ecosystem mostly had positive correlation with precipitation while negative correlation with temperature.

Effects of extreme drought on CO₂ fluxes of Zoige alpine peatland

ZHANG Yuan, HAO Yanbin, CUI Lijuan, LI Wei, ZHANG Xiaodong, ZHANG Manyin, LI Linfeng, YANG Si, KANG Xiaoming

2017, 34 (4): 462-470. DOI: 10.7523/j.issn.2095-6134.2017.04.008

Abstract ( 332 ) PDF (KB) ( 1 )

To study the effects of extreme drought on net ecosystem CO₂ exchange (NEE), ecosystem respiration (R_e), and gross primary productivity (GPP) of Zoige alpine peatland, the carbon fluxes in both extreme drought treatment (D) and control treatment (CK) were monitored by using static enclosed chamber technique in a control platform of extreme climate event. The results showed that extreme drought significantly decreased NEE, R_e, and GPP (P<0.05) of Zoige alpine peatland and hence reduced the carbon fixation capacity of targeted ecosystem. We also found that temperatures (air temperature (T_a) and soil temperature (T_s)) and soil water content (SWC) were the main driving factors of carbon budget dynamics in Zoige alpine peatland. NEE, R_e, and GPP were significantly positively correlated with air temperature (P < 0.05), and their sensitivity to the T_a change was weakened by extreme drought. The correlations of NEE, R_e, and GPP with topsoil temperature were much stronger than those with subsoil temperature. Besides, we found that extreme drought reduced the sensitivity of NEE to soil temperature at depth of 5 cm, but strengthened the sensitivity of R_e. Furthermore, NEE, R_e, and GPP were significantly positively correlated with soil water content (P<0.05). However, extreme drought had no significant effect on soil total carbon, nitrogen, and soil organic carbon contents (P>0.05).

Effects of biochar addition on nitrogen uptake of Glycine max and Arachis hypogaea seedlings

XU Xingliang, FENG Yuqing, CUI Jian

2017, 34 (4): 471-477. DOI: 10.7523/j.issn.2095-6134.2017.04.009

Abstract ( 351 ) PDF (KB) ( 2 )

¹⁵N-labeling technique was used to investigate effects of biochar addition (0, 0.5, 2.5, and 10 mg·g^-1) on biomass and nitrogen uptake of Glycine max and Arachis hypogaea seedlings. We found that biochar addition did not significantly alter total biomass of G. max seedlings compared to control, while a significant difference was observed between two higher addition levels. Biochar addition did not change total biomass of A. hypogaea seedlings, but the highest addition level significantly increased its root to shoot ratios. Increased biochar addition substantially reduced uptake of ¹⁵NH₄⁺ and ¹⁵N-glycine by G. max seedlings, but weak effect on uptake of ¹⁵NO₃^- was observed. Biochar addition significantly decreased uptake of ¹⁵NH₄⁺ by A. hypogaea seedlings, but did not significantly affect uptake of ¹⁵N-glycine. In contrast, uptake of ¹⁵NO₃^- by A. hypogaea seedlings increased first and then decreased with biochar addition. This indicates that biochar addition affects nitrogen uptake by crops, but the effect depends on plant species and amount of added biochar. Therefore, species and nitrogen forms should be considered when biochar is used as a management measure for agricultural soil to improve nitrogen use efficiency and crop production.

Peat sedimentation and its response to climate change of Huahu peatland on Zoige plateau

SU Qianqian, ZHU Dan, HE Yixin, YANG Zhen, ZHU Erxiong, JIANG Lin, XU Yingyi, PENG Changhui, ZHU Qiuan, CHEN Huai

2017, 34 (4): 478-486. DOI: 10.7523/j.issn.2095-6134.2017.04.010

Abstract ( 352 ) PDF (KB) ( 3 )

Natural radionuclide ²¹⁰Pb, soil water content, and dry bulk density data were used to calculate the geochronology and characterize the recent peat sedimentation rate of a soil profile obtained near Huahu lake on Zoige plateau. We analyzed the change characteristics of total organic carbon (TOC) content with depth and age, and calculated the recent rate of carbon accumulation (RERCA) of this peat section. It was concluded that the average peat sedimentation rate was 0.16 cm·a^-1 between 1824 and 2011, which is close to the reported values in other studies on Zoige peatlands. The weighted average sedimentation flux during this time span was 0.082 g·cm^-2·a^-1 and the RERCA was 86.12 g·m^-2·a^-1, which are comparable with the reported values in other researches. The differences indicate the specificity of the peatland formation and development. Using the climate data collected by the weather station, the data of mean annual temperature (MAAT) reconstructed by climate proxies in other researches, and the satellite observated climate data, we found that the main impact factor on climate change on Huahu peatland in recent decades was precipitation, which means that high annual precipitation in that region may contribute to the high carbon accumulation rate. Anthropogenic activities and other factors also constitute an interference in peat and carbon accumulation rate, which needs further study.

Respiratory CO₂ and CH₄ emission fluxes from naturally grazing female yak in eastern region of Qinghai-Tibetan Plateau during alpine meadow growing season

XUE Dan, XIONG Wan, HE Yixin, ZHU Dan, WU Ning, CHEN Huai

2017, 34 (4): 487-497. DOI: 10.7523/j.issn.2095-6134.2017.04.011

Abstract ( 254 ) PDF (KB) ( 2 )

In order to reveal the characteristics of the greenhouse gas emissions from naturally grazing female yak in Qinghai-Tibetan Plateau during the growing season, a combination of face mask and GC methods was used to measure the respiratory CO₂ and CH₄ emissions from three age groups of yak. The results showed that age had a significant impact on greenhouse gas emission rate and emission flux. Feeding significantly influenced CH₄ emission rate. The average emission fluxes of CH₄ and CO₂ in 1-2-year-old group were 54.59 and 2 663.71 g·head^-1·d^-1, respectively, and they were 80.48 and 3 715.17 g·head^-1·d^-1 in 3-4-year-old group and 84.45 and 4 663.55 g·head^-1·d^-1 in 5-6-year-old group, respectively. The respiratory CO₂ and CH₄ emission fluxes were positively correlated with yak biochemical parameters, which changed with age. The respiratory CH₄ emissions of yak are lower than bovine raised by freely grazing in other regions.

Effects of climate changes on plant phenology at high-latitude and alpine regions

MENG Fandong, ZHOU Yang, CUI Shujuan, WANG Qi, TSECHOE Dorji, WANG Shiping

2017, 34 (4): 498-507. DOI: 10.7523/j.issn.2095-6134.2017.04.012

Abstract ( 329 ) PDF (KB) ( 3 )

Phenology studies the timing of periodic phenomena of biological events, which is affected by biotic and abiotic factors. We review the main influences of climatic factors (e.g., temperature, precipitation, and timing of snowmelt) and species on plant phenology at high-latitude and alpine regions. Most previous studies indicated that warming and earlier snowmelt advanced green-up and first flowering but delayed senescence of individuals and community. The effects of precipitation on plant phenology were inconsistent. There were few studies on root phenology, and no general conclusions were obtained. Root phenology was affected by changes in soil temperature, moisture, and nutrient availability. The divergent responses found in magnitude and direction were mainly due to different measurements, sites, species, and ecosystems. Therefore, long-term ground observations of individuals and community phenological sequences are needed in order to deeply understand the processes and mechanisms of the effects of biotic and abiotic factors in the future. Ground observations of community phenology are particularly needed at high-latitude and alpine areas to match with remote sensing methods and scale from local site to large landscape. Furthermore, root phenology and biological mechanisms of phenological responses to climate changes should be studied.

Response and acclimation of photosynthesis in Nitraria tangutorum to rain addition treatments in temperate desert in Northwest China

BAO Fang, HE Ji, CAO Yanli, LIU Minghu, XIN Zhiming, WU Bo

2017, 34 (4): 508-514. DOI: 10.7523/j.issn.2095-6134.2017.04.013

Abstract ( 248 ) PDF (KB) ( 2 )

In this study, a field manipulative experiment was conducted with five simulated rain amount treatments (control, natural rain plus 25%, 50%, 75%, and 100% of multi-year mean precipitation) in a desert ecosystem in Northwest China, where the carbon cycle is extremely sensitive to the changes of rainfall amount and pattern. Photosynthesis and its temperature dependence in a desert shrub Nitraria tangutorum were investigated. The results are showed as follows. Rain addition treatments changed the magnitude of the photosynthetic acclimation to temperature in N.tangutorum. The apexes of the quadratic curves between photosynthesis rate and leaf surface air temperature shifted from about 29.31 ℃ in control plots to 28.87 ℃ and 28.57 ℃, in plots with 25% and 50% rain addition treatments, respectively. However, the apexes of the quadratic curves between photosynthesis rate and leaf surface air temperature shifted to 31.57 ℃ and 35.33 ℃ in plots with 75% and 100% rain addition treatments, respectively. The results will deepen our understanding of desert system carbon cycle.

Contents and output characteristics of dissolved carbon in water body of alpine forest headwater streams in rainfall season

ZHANG Yu, YANG Wanqin, TAN Bo, LIANG Ziyi, WU Fuzhong

2017, 34 (4): 515-520. DOI: 10.7523/j.issn.2095-6134.2017.04.014

Abstract ( 322 ) PDF (KB) ( 2 )

Dissolved carbon flow from water in the alpine forest headwater streams is one of the essential components of carbon flux. A study on dissolved carbon output with water flow in the alpine headwater streams was carried out in a typical alpine forest in the eastern Qinghai-Tibet Plateau in July 2015. The output characteristics of dissolved carbon with water flow were investigated in the catchment covering an area of 4.31 km². The results are given as follows. The maximum annual output rate of dissolved carbon in unit area catchment was 12.99×10³ kg·km^-2. The output rates of the unit area of catchment were 3.56×10^-2 g·m^-2·d^-1 for total carbon, 2.12×10^-2 g·m^-2·d^-1 for inorganic carbon, and 1.43×10^-2 g·m^-2·d^-1 for organic carbon in the alpine forest headwater streams. In contrast, the output rates of the unit area of stream were 2.01×10³ kg·m^-2·d^-1 for total carbon, 1.20×10³ kg·m^-2·d^-1 for inorganic carbon, and 0.81×10³ kg·m^-2·d^-1 for organic carbon. For streams with length greater than 30 m, total carbon and inorganic carbon concentrations were higher in stream source than at stream end, but organic carbon concentration showed the opposite. Contrarily, for streams with length less than 30 m, the concentrations of total carbon, inorganic carbon, and organic carbon had larger values at stream end than in stream source. These results suggest that the water flow in the alpine forest headwater streams leads to a large amount loss of dissolved carbon. This study provides a new idea for further studies on the ecological linkage between the land system and water body under the climate change.

Dynamics on humic acid and fulvic acid in the stump systems with different log years in the Pinus massoniana plantations

ZHOU Jiao, YANG Wanqin, WU Fuzhong, TAN Bo, DUAN Fei, LIU Hui

2017, 34 (4): 521-528. DOI: 10.7523/j.issn.2095-6134.2017.04.015

Abstract ( 294 ) PDF (KB) ( 3 )

The turnover of humic acid (HA) and fulvic acid (FA) during stump humification plays crucial roles in sequestering carbon and maintaining soil fertility in plantation ecosystems, but little related information has been available. A field experiment was conducted in Masson pine (P. massoniana) plantations in Sichuan Basin. The decaying stumps were sampled based on the local log file records from 1999 to 2013, and the stump system was further divided into stump wood (SW), stump root (SR), bark (B), and linked roots (Rn) with different diameters. After 15-year decomposition, HA concentration and HA/FA in the stump system increased significantly, while the stocks of HA and FA and FA concentration in the stump system decreased significantly. The stocks of HA and FA in the stump system ranged from 1 688.35 to 4 434.99 kg·hm^-2 and from 822.86 to 6 159.29 kg·hm^-2, respectively, in the Masson pine plantation. SR had higher HA and FA stocks than SW and B. Moreover, the roots with larger diameter had higher HA and FA stocks than those with smaller diameters. In conclusion the stump system in the Masson pine plantation has high stocks of HA and FA and the humification degree increases in decaying process. The results provide basic information for understanding the processes of coarse wood debris decomposition and carbon sequestration in the plantations.

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